Traffic management in mobile cellular networks comprises a set of features whose final purpose is the redistribution of the mobile devices in the cells so that the probability of congestion and blocking is reduced and, thus, capacity is increased and quality is improved.
In current systems, the design is based on the hypothesis of a uniform distribution of served mobile devices. However, such assumption may be far from reality. Namely, the flexibility resulting from the existing large set of parameters included in the different algorithms related to traffic distribution can not be fully seized because of its complexity. The large set of available parameters makes the detailed planning process on a cell-by-cell basis a time-consuming work.
As a consequence, operators fix parameters to a common set of default values shared between the cells even if the performance and capacity is not achieved in an optimum way. Moreover, a few operators extend the parameter optimisation by classifying the cells in accordance with certain scenarios like rural, urban, tunnel, indoors etc. and/or in accordance with the layer/band used (like Macro900/1800, Micro900/1800, Pico1800, Motorway900). So, the cells are divided into scenario groups or layer/band groups, and common default parameter values are shared which, however, are not optimum.
In those cases where existing features for traffic balance and congestion relief are difficult to optimise, just a few parameters are taken into account for optimisation which requires so-called field trials. During the tuning process, conclusions from parameter changes are difficult to derive, and final settings are nearly always on the safe side with its limited results. Moreover, such trials are normally focused on global parameters of features under study, and parameter optimisation of adjacent cells is hardly ever done. So, differences between adjacent cells are rarely considered due to a high effort required. Therefore, the potential of so-called adjacency parameters is not fully exploited.
A final limited parameter tuning based on cell/area level performance indicators is normally carried out only over those cells where performance problems are existing.
Even if an optimum value were reached by means of the above-mentioned trials, changes in traffic or environment conditions, like the installation of new cells, changes of interference level by frequency re-planning etc., would force a further re-tuning process of the parameter base, where no automatic reactive process is currently in use. Such a situation could be analysed as a result of slow trends, like the change of the number of user registrations, or fast changes, e.g. of the number of connections, during a short time period, like an hour or a day.
One of the critical causes of network variations is interference. Differences in propagation conditions between cells or changes in the frequency plan will produce variations in time or space. Adaptation to this variations would increase network performance, but would also require a very high tuning effort.
U.S. Pat. No. 5,241,685 A discloses a load sharing control for a mobile cellular radio system so as to achieve a load sharing between a first cell and a second cell adjacent to the first cell where each cell is serving a number of mobile devices. The first cell has a predetermined entering threshold which is a function of the received signal strength for mobile devices entering this cell from the second adjacent cell by means of handoff. A certain occupancy level indicates the occupied channels in relation to the available channels in the cell. For handover, the occupancy level of the first and second cells are determined, and it is further determined whether the second cell has a lower occupancy level than the first cell. Then, an entering threshold level for the second cell is determined which is a function of the received signal strengths for the mobile devises in the first cell about to enter the second cell. The entering threshold for the second cell is decreased if the occupancy level of the second cell is found to be lower than the occupancy level of the first cell, whereby the border between the first and second cells is dynamically changed. So, in this known system, the redistribution of the users for congestion relief is usually achieved by shrinking loaded cells through temporarily reduced margins for handovers between adjacent cells.
However, this prior art system has the disadvantages of reduced quality in traffic receiving cells and reduced overlapping in activation periods wherein the latter results in ping-pong problems.